Method of making a rotor

ABSTRACT

A rotor especially for use in a high speed electric motor/generator comprises fibre-reinforced plastics material incorporating magnetic filler material, the fibre-reinforced plastics material being arranged as a multi-layered cylindrical portion of the rotor, the magnetic filler material being disposed within and between the layers. The said cylindrical portion may be a hollow tubular-portion. The said portion may be enclosed in a non-composite eg, wear resistant, layer.

This is a divisional of application Ser. No. 08,232,268, filed Jul. 6,1994, now U.S. Pat. No. 5,477,092.

A ROTOR

This invention relates to a rotor, and more particularly but notexclusively, to a rotor for use in high speed applications.

High speed rotors have been proposed for use in a number of applicationsparticularly as electric motor/generators. They can act as a motor orgenerator depending on whether electrical energy is being fed into orextracted from an electrical coil on a stator associated with the rotor.Such an arrangement is proposed for example in FR 2614367 as a means ofenergy storage and conversion.

Prior art rotors for motor/generator applications have constructionswhich are not ideal for high speed applications.

According to the present invention, there is provided a rotor comprisingfibre-reinforced plastics material incorporating magnetic fillermaterial, the fibre-reinforced plastics material being arranged as amulti-layered cylindrical portion of the rotor, the magnetic fillermaterial being disposed within and between the layers. The saidcylindrical portion may be a hollow tubular portion. The said portionmay be enclosed in a non-composite, eg wear resistant, layer.

Rectors of the present invention beneficially allow an efficientelectromagnetic interaction between the rotor and a neighbouring statorto be maintained along the length of the body of the rotor and out ofbalance regions in the rotating mass can be avoided when the rotor isemployed at high speeds.

Preferably, the said portion in the rotor according to the presentinvention comprises a first layer of windings of fibres, at least oneintermediate layer of windings of fibres superimposed thereon anddefining helical spaces therebetween, magnetic filler material in thespaces, and an outer layer of windings of fibres superimposed about theintermediate layer(s).

The said portion might be superimposed on a substrate.

The said plastics material may comprise any one or more of the knownmatrix materials employed in fibre reinforced composite materials. Forexample the material may comprise a thermosetting or cold setting orthermoplastic polymeric material, eg selected from one or more of epoxyresins, polyester resins, Friedel Crafts resins, polyimides, polyamides,polyether sulphones and polyether ketones (PEEK) optionally togetherwith known hardeners, fillers and the like. The fibres may be wound as acollection in tows. They may be wound helically and/or in hooped fashionwithin the composite.

The invention also provides a method of manufacturing a rotor, themethod including the steps of:

a) winding onto a mandrel an initial layer comprising resin-impregnatedfibres;

b) winding at least one intermediate layer comprising resin-impregnatedfibres about the initial layer so as to define spaces between the fibresof the intermediate layer;

c) disposing a mixture comprising magnetic filler material and a resinmatrix material in the spaces;

d) winding an outer layer comprising resin-impregnated fibres about theintermediate layer;

e) applying a magnetic field to align the magnetic filler material in arequired orientation whilst the resin is in the liquid state prior togelling and during the gelling process;

f) curing the resin, and

g) magnetising the magnetic material.

The resin may be a thermosetting resin and curing may be carried out byheating to an appropriate known curing temperature; cooling may followstep f) before step g).

Preferably, the fibres comprise carbon fibres, or may comprise glassfibres, or Kevlar (polyaramid) plastics or aluminium tape, boron, nylon,polyolefin or mixtures of these or any other suitable known fibres.

The magnetic material employed as the said magnetic filler material maycomprise particles, spheroids, whiskers, fibres or the like. Desirably,the material is a powder material. The magnetic material may compriseiron, nickel, cobalt or an alloy containing one or more of these. It maycomprise a ferrite, eg barium ferrite. Alternatively, and preferably,the material comprises a known hard magnetic material (ie hard tode-magnetise) comprising a rare-earth element, eg cobalt-samarium orneodymium-boron. The magnetic material may suitably be incorporatedbetween tows of fibres within the composite.

It will be understood that the invention also includes a rotor having aportion thereof made by the method of the invention, and an electricmotor or an electric generator or a combined motor-generatorincorporating the rotor.

Fibre reinforced composites containing magnetic material for rotatingcomponents are known in the prior art eg GB 1370655 and U.S. Pat. No.4,508,567 but these prior art devices are for different essentially lowspeed applications. The construction and manufacture of the novel rotorsof the present invention for high speed electric motor/generators isquite distinct from such prior art devices. The rotors of the presentinvention can provide accurate position control, high electricalefficiency and ultra-high speed capacity in an electric motor/generator.The use of composites in rotors in the novel manner described hereinpermits a very high strength construction to be obtained which canwithstand high speeds.

Embodiments of the present invention will now be further described byway of example only with reference to the accompanying drawings, inwhich:

FIG. 1 shows a side sectional representation of a rotor about a stator;

FIG. 2 shows to an enlarged scale that part of the rotor within the area`X` of FIG. 1;

FIG. 3 shows a diagrammatic representation of an application of therotor and stator of FIGS. 1 and 2, and

FIG. 4 shows an application of a modified form of the rotor and statorof FIGS. 1 and 2.

Referring now to FIG. 1, an electric motor 8 is shown comprising ahollow cylindrical rotor 10 about a cylindrical stator 11 of laminatedconstruction and which has end spigots 12, 13 for location in supports14, 15. End rings 16, 17 at the ends of the rotor 10 hold the rotor 10captive on the stator 11. A central blind hole 18 in the stator 11communicates with a number (seven are shown) of radial holes 19 whichexit at a narrow air bearing space 20 (not shown in FIG. 1) between therotor 10 and the stator 11. Electric coils 21 (only one is shown) aredisposed in the stator 11 to provide an electric field to drive therotor 10. A hole 22 in the support 15 communicates with the central hole18 to provide a feed path for air to the air bearing space 20.

As shown in more detail in FIG. 2, the rotor 10 comprises an inner shell30, and an outer shell 31 superimposed on the inner shell 30. Twointermediate layers 36, 37, each comprising tows 38, 39 respectively ofcarbon fibres in an epoxy resin matrix, are wound circumferentially atthe same helix angle but displaced angularly 180° out-of-phase about thelayer 32. Spaces 40, 41 respectively between the tows 38, 39 are filledwith a composite 44 comprising magnetic material powder held in an epoxyresin matrix. An outer layer 46 comprising tows 48 of carbon fibres inan epoxy resin matrix is wound circumferentially closely together on theintermediate layer 37. A final wear resistant (eg chrome) layer 50 issuperimposed on the outer layer 46.

In use of the motor 8, air is fed through the holes 22, 18 and 19 to theair bearing space 20 to support the rotor 10. The coils 21 are energisedand the resulting electric field rotates the rotor 10. Because of thelight weight of the rotor 10 extremely high rotational speeds can beattained, ie. above 20,000 rpm (eg, 100,000 rpm), although the rotor 10may be used below these speeds.

In one application of the motor 8 in the printing industry as shown inFIG. 3, the motor 8 (not shown) is disposed opposite and adjacent to anidler roller 55 so as to feed between them paper 57 from a roll 60supported on an idler bearing 62. The motor 8 allows the tension of thepaper 57 to be controlled.

An application of the rotor of the invention as an electric generator isshown in FIG. 4. In FIG. 4, a generator 65 shown has a rotor 66 similarin most respects to the rotor 10 of FIGS. 1 and 2 and disposed about anupright internal stator 68. The internal stator 68 is similar in mostrespects to the stator 11 of FIG. 1 but has a flat upper end 70 fromwhich an end disc 72 of the rotor 66 is displaced by an air bearingspace 74. A shaft 76 from the end disc 72 extends through a gas thrustbearing space 77 for connection to a drive unit (not shown), for examplea gas turbine. An external stator 78 about the rotor 66 defines a gasbearing space 80 between them. The external stator 78 has electric coils82 whilst electric coils 84 are disposed in the internal stator 69. Thelower end of the internal stator 68 defines a spigot 86 which locates ina base 88.

In use of the generator 65, rotation of the shaft 76 drives the rotor66, thereby generating electric current in the coils 82, 84.

A example of suitable magnetic material powder is cobalt samarium butother magnetic material powders may be used.

It will be understood that alternative fibres, for example glass fibres,may be used in the rotor 10, 66. It will also be appreciated that therotor 10,66 may comprise only one shell or more than two shells, and maybe just one or more than two intermediate layers of windings.

One method of forming the rotor 10 will now be described.

Using a conventional fibre winding machine, tows 34 of carbon fibres ofthe initial layer 32 of the inner shell 30 impregnated with uncuredepoxy resin are wound onto a rotating mandrel. The intermediate layers26, 37 of tows 38, 39 of carbon fibres impregnated with uncured epoxyresin are wound onto the inner layer 32 with a 180° out-of-phaserelationship to one another. The spaces 40, 41 between the tows 38,39are filled with the composite 44 comprising magnetic material powder ina demagnetised state and uncured epoxy resin. The outer layer 46 of tows48 of carbon fibres impregnated with uncured epoxy resin is wound ontothe intermediate layer 37. The outer shell 31 is formed in a similarmanner with the exception of the wear resistant layer 50. A magneticfield is applied in a known way so as to align the magnetic materialpowder in the composite 44. Finally, the epoxy resin is cured in anappropriate heating environment. The outer shell 31 is machined to size,removed from the mandrel, and the end rings 16, 17 attached using asuitable adhesive eg Araldite (Trade Mark). The wear resistant layer 50is then applied. The rotor 10 so formed is magnetised using a suitableelectric coil to convert the magnetic material powder in the composite44 into its permanent magnetised state.

The rotor 66 is made in a similar manner, except that the end disc 72 isattached to the inside of the rotor 66 using a suitable adhesive (egAraldite).

An alternative wear resistant layer 50 such as glass fibre reinforcedcomposite, or ceramic material may be used.

Instead of the rotor being of hollow form, the shells 30, 31 may besuperimposed on a substrate (eg aluminium) to form a composite rotor.

I claim:
 1. A method of manufacturing a rotor comprisingfibre-reinforced plastics material incorporating magnetic fillermaterial, the fibre-reinforced plastics material being arranged as amulti-layered cylindrical portion of the rotor, the magnetic fillermaterial being disposed within and between the layers, the methodincluding the steps of:a) winding onto a mandrel an initial layercomprising resin-impregnated fibres; b) winding at least oneintermediate layer comprising resin-impregnated fibres about the initiallayer so as to defined spaces between the fibres of the intermediatelayer; c) disposing a mixture comprising magnetic filler material and aresin matrix material in the spaces; d) winding an outer layercomprising resin-impregnated fibres about the intermediate layer; e)applying a magnetic field to align the magnetic filler material in arequired orientation whilst the resin is in the liquid state prior togelling and during the gelling process; f) curing the resin; and g)magnetising the magnetic material.